This invention is generally directed to developer compositions and processes for formulating stable toner and developer compositions. More specifically, the present invention is directed to a process for obtaining colored toner compositions with stable triboelectric charging values by subjecting the carrier particles to be admixed with the aforementioned toner to treatment, or preconditioning with a metal salt of a fatty acid, or a metal salt. Therefore, in one enbodiment the present invention is directed to a process for the formulation of developer compositions, which comprises treating coated carrier particles, especially ferrites, with metal salts of fatty acids such as zinc stearate; and thereafter admixing the resulting pretreated carrier particles with a toner composition comprised of resin particles, pigment particles, and preferably optional additive particles. The aforesaid carrier pretreatment process step enables in one embodiment of the present invention the resulting negatively charged colored toner compositions to possess substantially identical charging characterisftics, decreased aging over extended time periods, insensitivity to relative humidity, and improved admixing characteristics. Accordingly, the toner and developer compositions of the present invention are particularly useful in permitting the development of colored images in electrophotographic imaging and printing processes. Specifically, thus the developer compositions illustraed herein can be selected for generating colored images while retaining stable trioelectric characteristics. Furthermore, in accordance with the present invention there are provided toner and developer compositions wherein each of the separate colored toner particles, inclusive of cyan, magenta, and yellow, age at substantially the same rate permitting developed prints with the same color intensity beginning wit the first printing or imaging cycle and continuing for an extended number of cycles. Furthermore, the toner compositions of the present invention contain in addition to the treated coated carrier particles, in one important aspect of the present invention, toner particles containing metal salts of fatty acids such as zinc stearate or metal salts, which toners have the improved characteristics as mentioned herein, including excellent charging performance and insensitivity to relative humidity of from about 20 to about 80 percent. Furthermore, the toner and developer compositions of the present invention can be selected for ionographic imaging processes, that is those processes wherein, for example, electroreceptors are selected, reference for example the Delphax 4060.TM. commercially available printer.
Numerous different toner and developer compositions are known including those containing styrene butadiene copolymers, reference U.S. Pat. No. 4,469,770, the disclosure of which is totally incorporated herein by reference. Also, toners with acceptable admixing characteristics are illustrated in U.S. Pat. No. 4,524,120, the disclosure of which is totally incorporated herein by reference, wherein the carrier selected for admixing with the aforementioned toner contains a continuous polymer coating thereover having incorporated therein a fluoropolymer.
Futhermore, there is described in a number of patents the selection of metal salts and metal salts of fatty acids as external additives for toner compositions, reference for example U.S. Pat. No. 3,590,000, the disclosure of which is totally incorporated herein by reference, which illustrates the use of, for example, zinc stearate as an external additive for toner compositions; 3,655,374; and 3,983,045, the disclosures of which are totally incorporated herein by reference.
Of particular interest are the teachings in U.S. Pat. Nos. 4,331,756 and 3,740,334. In the '756 patent there are disclosed developer compositions with toners and carriers containing thereover certain coatings such as mixtures of butadiene acrylonitrile rubber, reference column 4, lines 1 to 11, for example. In column 2, lines 33 to 46, of this patent it is indicated that if it were possible to coat the carrier with zinc stearate, the characteristics thereof would remain constant, see column 2, line 41. At line 43 in column 2, it is indicated that as a practical matter this is not possible since the abrasive action of the constantly moving developer continuously removes the zinc stearate. In the '334 patent, column 7, lines 68 to 75, for example, it is indicated that the metal salts may be tumbled or milled with the toner or carrier particles or intimately dispersed in each toner or carrier particle. Also, in column 8, lines 36 to 38, it is indicated that the metal salt of a higher fatty acid can be physically mixed with or applied as a coating on the toner or carrier particles, preferably in an amount of about 0.02 to about 10 percent. Also of interest in U.S. Pat. No. 4,374,192, a divisional of the aforesaid 4,331,756 patent; and U.S. Pat. No. 4,265,995.
Additionally, the Xerox Corporation 6500.RTM. copying machine selects separate toner compositions, inclusive of a magneta toner composition, a cyan toner composition, and a yellow toner composition. It is known that in some instances with the 6500.RTM. images of poor copy quality result. Thus, these images have undesirable background deposits, and low densities unless the bias on the developer mixtures is adjusted, resulting from different triboelectric charging properties as each of the colored toner compositions age. This problem is eliminated with the toner compositions of the present invention in that there can be achieved substantially similar stable triboelelectric charging characteristics for the colored toner compositions primarily as a result of the presence of the pretreated carrier particles. Furthermore, only a limited number of useful colored pigments are available, therefore, substantial efforts have been consumed in affecting adjustments to the aforementioned colored toner compositions for enabling improved copy quality with extended usage.
Accordingly, there continues to be a need for the formulation of stable toner, and developer compositions. More specifically, there is a need for negatively charged toner compositions, and processes that will enable the preparation of electrically stable toner compositions. There is also a need for processes of formulating colored toner compositions wherein each of the separate toners generated are of substantially equal triboelectric charging values. Further, there is a need for colored toner compositions wherein the resulting separate toners generated do not significantly age with an extended number of copy cycles. Additionally, there is a need for magenta, cyan, yellow; highlight colors such as red, blue, and green; toner compositions with similar triboelectric charging characteristics; and wherein these characteristics are maintained for an extended number of imging cycles. There is also a need for colored toner compositions with improved stable electrical properties thereby enabling substantially similar color intensities for an extended number of imaging cycles. Moreover, there is a need for negatively charged colored toner compositions with rapid admix charging times of, for example, less than one minute, and preferably less than about 30 seconds. Furthermore, there is a need for negatively charged colored toner compositions with a stable constant triboelectric charge thereon of from about 15 to about 35 microcoulombs per gram. Moreover, there is a need for negatively charged colored toner compositions which are insensitive to relative humidity, and possess improved admix charging characteristics, which toner compositions contain metal salts or metal salts of fatty acids, and wherein the coated carrier particles also include metal salts or metal salts of fatty acids, particularly zinc stearate.